Protected motor



July 4, 1939. v. WEBER 2,165,082

PROTECTED KOTOR Filed Aug. 1, 19156 1%. z l i //2 /4 /0 2 v7-ART` 'Z5 f6 |537 www 1| .9 /3g40 FrR/FUGAL .5w/rch' `3/ l//cTo/e WEBER,

M2M/4W Patented July 4, 1939 PROTECTED MOTOR' Victor Weber, St. Louis, Mo., assignor to The Emerson Electric Mig. Co., St. Louis, Mo., a corporation of Missouri Application August 1, 1936, Serial No. 93,794

2 Claims.

The present invention relates to a combination of electrical energy-translating devices, and means to deenergize the same upon occurrence of excess current or heat therein. As a particular application to which it is especially adaptable, the combination can comprise an electric motor and a thermally actuated switch mounted within the motor casing and opened when the heat produced in the motor exceeds a predetermined limit, the heat being generated by sudden excess of currents within the motor windings acting upon a heater element in the switch, or by gradual accumulation of heat in the windings.

An object of the present invention is to provide l5 a motor having' a thermally-actuatable circuit breaker mounted withinr the motor casingl and operatively .connected therewith to control energization of the motor.

Another object is to provide a motor having a thermally-actuatable circuit breaker and an associated heater element operatively connected therewith to break the line circuit, either upon a predetermnately excessive current in the wind ings, or upon undue rise of heat in the motor casing.

Another object is to provide a motor having a thermaily-actuatabie circuit breaker and-associated heater element connected therewith to protect the windings during starting from an excessive current.

Another object is to provide a multiple winding motor having a heater element connected in transformer relation to the main windings, and

disposed in heat/#transferring relation to a therg5 mally-actuatable circuit breaker controlling the energization of the motor.

Another object is to provide a multiple windings motor having a heater element connected in auto-transformer relation to the main wind 49 ings, and disposed in heat-transferring relation to a thermaly-actuatable circuit breaker controlling the energization of thc'znotor.

Other objects and advantages will appear from the following description, takenin conjunction 45 with the accompanying drawing, in which- Fig. 1 is a diagrammatic view of the combination of motor windings and the thermal switch circuit with its associated heater element.

Fig. 2 is a similar view with a somewhat diier- 5g ent heater element circuit.

Inthe modification shown in Fig. 1, the line terminals of the motor are indicated at I0 and I, they being on a suitable part of the-motor casing I2. The remainder of the motor casing 55 is represented by the broken line I2 which sur- (Cl. FIZ- 279) rounds the to be described elements,`thereby indicating s aid elements are within the motor casing I2. Within the motor casing are the convcntional main and starting windings, as shown. From the terminal member I0 extends a lead I3 g that divides at I4 into the parallel main and starting windings. The main circuit is shown as having two pole windings I5 and I6, they being in series. From a'n end of the winding I6 extends a line I'I to a junction I8. From this juncl@ tion a line I9 extends to a switch 20, from which switch extends a line 2i to the other motor terminal II.

The starting winding likewise comprises two pole coils 24 and 25 that are connected in series B5 'from the junction I4. From an end of the coil 25, a lead 26 extends to a condenser 2l ordinarily used in such circuits. From this condenser, a line 28 extends to a pole 29 of a two-pole centriiugal switch 39. From switch tti, a line 3l a' extends to the junction I8 so that the starting circuit is shown to be in parallel with the main circuit.

From a suitable point, as 33, in the line o the main windings, is tapped off a lead 3@ extending gg to a two-pole secondary having windings and 3S located in inductive relationship to the main pole windings I6 and I5, respectively. From the winding 36 extends a. lead 3T to a heater coil 38. From the heater coil 38, a line 39 connects to the 3@ other pole 40 of the centrifugal switch. It will be understood that the switch 20 is a thermal switch that opensautomatically when the temperature reaches a predetermined value.l Such a switch is shown in my copending application Serial No. as 86,991,'1i1ed June 24, 1936. The heating element 38 is in heating relationship with the thermal element of the switch. This is indicated by the backing element 4I upon which both the heater 38 and the switch 20 are mounted. 4o

The operation of this device is as follows:

When the motor circuit is turned on with potential supplied to the terminals I0 and II, current will flow through the lead I3 to the junction I4,

at which point it divides into the main and the starting circuits. It is to be understood that the starting windings are mechanically phasedisplaced from the main windings so as to produce a starting torque within the motor. The current from the starting windings flows through 5c the centrifugal switch 39 and joins with that in the main windings atthe junction I8, whence it ows by way of the thermal switch 20 back out at the terminal II. As the motor Vis starting, owing to the low back E. M. F. within the main f ere is relati1 ely his' through. result that, in the secondary windings fio and l there is a high induced M. and consegne-n ly a large current flowing through the heater T;l the motor gets up to sneed with normal rapidity, the duration of this high current iii the heater is insucient to onen the switch. En nomal operation oi the motor, the centrifugal switch will open as soon as motor attains the desired speed, so that the starting windings and the heater circuit are opened. At this time, only the nialn windings will then be energized. However, if, 'for ang7 reason, an excess current dotre through the main windings, such as would loe caused hy overload on the motor slowing it down, lout not to the sneed at which the centrifugal switch operates, the bach iti. Within, the main windings i and UG will loe greatly reduced, since, under these conditions, the rotor windings are ineective to produce such a .'oaclr E. M. When this occurs, a large current williiow in the main windings. Ir" this current accumulates sufcient heat by flowing for an extending period ci time, a quantity of heat might loe generated Within the Windings and motor casing suiicient to he dangerous to the winding. However, with the present arrangement of the switch Within the motor casing, the heater element will respond to this heat and open the switch thus shutting-down the motor.

"if the motor is blocked, the centrifugal switch will close, closing the heater circuit. when this occurs. the larg-e current yilowng through the main windings produces a correspondingly high secondary windings and rhe high current produced in the secondary windings will flow through heating coil to the terminal il@ ci centrifugal switch; thence through line Si to the junction it; and haci: by Way oi line il, junction and lead il@ into the secondary windings, heater will then rise in temperature, and act on the switch 2li to open the saine, in a very short time. it is,

.ci course, understood that the characteristics of the secondary circuit are out ci phase with those of the main windings. thermore, they are so much smaller in value than those of the main circuit that they do not materially ahect the latter.

in the present description, it will loe observed that the secondary winding has heen divided into the samenum-oer ci parte as the primary, namely, a winding for each pole oi' the ,ordinary or niain Winding o\the motor. the alteration in flux caused the secondary equally; divided over the poles of the main windings. if this is not done, and the alteration is concentrated on one or more asymmetrical poles, a consequent magnetic unha-lance in the motor is act to produce undesirable noise. viiice the present' device shows two poles, the use oi two secondary Windings produ-ces a symmetrical diwleion ci the secondary. 'While improvement results from the division oi the secondary among symmetrical poles over a division asymmetrically, it is found most desirablew to divide the secondary among all the poles of the windings. Asa matter oi fact, however, any division will reduce the intensity of the imbalance, and consequently reduce the noise.v

it is, therefore, evident that, the motor is completely blocked, the switch will open because of the excess current in the :main windings and the heat produced in the heater Sil by such excess current. Likewise, should` at any time casing 552,

the heat generated Within the motor casing for any reason exceed this predetermined value, the switch il@ will open. Since this switch opens the main line to the windings or" Athe rector, the motor will automatically ne stopped.

ln the modification shown in Fig. 2, motor terminals are shown at and 5i on the Walls oi a motor casing The remainder or the motor casing is represented hy the broken line 52 which surrounds the to be described elements, thereby indicating said elements are Within the motor Within the motor casing and from the terminal 5D extends a lead to a junction point 55. From this junction point 5G extends the main winding a small-portion o which is separately designated for reasons to be described. From'this 'winding extends a line to a junction from which junction it continues by Way oi line throughs switch t@ and a line hack to the other terminal 5i. rThe switch 6@ is, in all respects, identical with the switch 2li.

Likewise, from the iuncticn is led the starting Winding circuit in parallel with the main winding circuit. in this circuit is the starting winding will from which a line extends to a condenser Frein condenser, a line connects-to a pole ci a two-noie centrifugal switch' I. From this switch, a line ril connects to the junction so that the starting circuit closes through the switch Si] to the terminal Tapped into the main windings, at some suitable point 13, dividing the section aforesaid, is a lead Jl passing through e. heating element 7S actuating switch and, ley Way ci a line to the other pole 8@ of the centrifugal switch. il switch hacking plate is shown in the operation oi tins modification, the princigoles are the san/le ci Fig. l, since both comprise ihductance circuits hy :means or which a certain variable out alt-Veys low current may flow through the heating elements and it. Furthermore, amount ci" this current in Fig. 2, similarly to Varies with the amount oi current owing in the main windings. Whereas Fig. i shows e iull transformer, 2 shows an auto-transformer. Ein Fig. 2, the current flowing in the auto-transformer circuit is much less than that owing in the main winding, by Virtue oi the small number oi coils in. the portion 5t.

Vl'lence, only a small eiect is produced on the main winding by the action or" the auto-transyiorrner. g

The general operation ci this circuit then is identical with that oi the circuit -oi Fig. l and need not be described in further detail. Both circuits include a heater operable on low voltage and lootii act to open their respective switches when the current i'iowing in the main or the main and starting windings is excessive to a point of danger. Likewise, in Tooth cases, the switches l will open 'when the ambient temperatures Within themotor casing exceed this critical value.

lily connecting the heater to he energized off the main Winding, the switch will he opened if the starting winding circuit is broken, such as might occur upon failure of the condenser 2l (or iii). 'in such case, the motor switch is closed, and the phase circuit does not energize, the motor cannot start, and a high current will :dow in the main windings. The presence of the switch as described -will prevent damage to the main winding by opening the ,circuit in a very short period of time.

What is claimed is:

l. in combination with a motor having main and starting windings, a circuit for said main windings, a circuit for said starting windings, means joining said circuits comprising a pair of lines adapted for connection to a power source, a heater element, means connecting said heater ,element to said main winding circuit so that there is induced from said main windings as a primary through said heater element a potential producing a current proportional to that in said main winding, means for deenergizing said starting winding and said heater element when the motor attains a desired speed of operation, and a switch in one of said power lines actuatable by said heater element.

2. In combination with an electric motor having starting and running windings, a thermallyactuatable switch for controlling said motor mounted within the motor casing in heat-receiving relation to the windings, and a heater element located in heat-transferring relation to the switch connected in auto-transformer circuit with the main windings to receive current produced by the back E. M. F. of said windings and through a terminal of a. centrifugal switch, which is in series with the starting winding,` for energization during the starting of the motor, said 'heater being adapted to effect opening of the thermallyactuable switch during starting ofthe motor when an abnormal line current is supplied to the motor circuits.

-' VICTOR WEBER. 

